Effect of n-alkyl and sulfonyl groups on the wetting properties of comblike poly(oxyethylene)s and stick-slip behavior

The influence of side chain length and sulfonyl moiety on the molecular structures and wettability behavior of poly(oxyethylene)s with alkyl sulfonyl side chains (CH(3)-nSE, n = 1, 2, 3, 4, 5, 6, 8, 10), where n is the number of the carbon atom in the n-alkyl side group, was investigated. CH(3)-nSEs having shorter side chains (n < 5) do not have ordered structures, and their surfaces were found to be more polar than those of CH(3)-nSEs having longer side chains (n ≥ 5). The CH(3)-nSEs having longer side chains show double-layered lamellar structures (n ≥ 5) with well-aligned side chains and low surface energies in the range 21.2-25.8 mN/m. Interestingly, stick-slip behavior was observed only on the surfaces of CH(3)-3SE and CH(3)-4SE when water was used as the test liquid. The surface deformation at the three-phase line was generated from interactions between water and sulfonyl groups, and the optimum side chain lengths were believed to cause the stick-slip behavior.     

Wettability of the morphologically and compositionally varied surfaces prepared from blends of well ordered comb-like polymer and polystyrene

Phase-separated surfaces of blends of polystyrene (PS) and well ordered comb-like polymer, poly[(oxy(decylsulfonylmethyl)ethylene)] (CH(3)-10SE), were prepared by spin casting polymer mixtures. Various surface morphologies, such as holes, islands, connected islands and pillars, were prepared by changing the blend compositions. Due to the influence of the CH(3)-10SE domain with a well ordered molecular conformation, a very low energy surface (≈22mN/m) was created, which is close to the value of the pure polymer (≈20mN/m), even when the blends contained only 20wt.% of the pure polymer. Furthermore, by selective etching the PS domain in the blend surfaces, the advancing contact angles of water and n-hexadecane were highly increased from 113.5° and 43.2° for the pure CH(3)-10SE surface to 133.3° and 67.2° for the CH(3)-10SE structural surfaces with holes prepared using the solvent etching method, respectively. The result of the water advancing contact angles measured on the samples immersed in water over 20days showed that the film stability of CH(3)-10SE could be improved considerably by even adding small amounts of PS.     

Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m² generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer.     

Homogeneous liquid crystal alignment on poly(vinylidene fluoride-trifluoroethylene) films subjected to ion-beam irradiation

We demonstrate homogeneous and uniform liquid crystal (LC) alignment on poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] films using ion-beam (IB) irradiation and a performance improvement of twisted nematic (TN) cells using IB-irradiated PVDF-TrFE films. Spontaneous ferroelectricity of the PVDF-TrFE films was modified by IB irradiation, which affected the LC alignment properties. The variation in the pre-tilt angles of the LC molecules on the IB-irradiated PVDF films is attributed to surface reformation, including defluorination and oxidation because the pre-tilt angles of LC molecules can be controlled by adjusting the fluorine content. The results of contact angle measurements supported this phenomenon. A 58% reduction in the switching voltage was observed for TN cells, indicating that the IB-irradiated PVDF-TrFE films are a promising candidate for use as an alignment layer.     

Liquid crystal alignment properties of poly(styrenesulphonate)/alkyltrimethylammonium complexes

We synthesised a series of poly(4-styrenesulphonate)/alkyltrimethylammonium (PSS-#Cx, # = 12, 14 and 16; x?=?80, 60, 40 and 20) complexes, where # is the number of carbon atoms in the alkyl groups in alkyltrimethylammonium bromide, and x is the molar content (%) of alkyltrimethylammonium moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a longer alkyl side group and a higher molar content of alkyl side group showed homeotropic LC alignment behaviour with a pretilt angle of about 90°. The homeotropic LC alignment behaviour was well correlated with the surface energy of the polymer films. Homeotropic LC alignment was observed when the surface energy values of the polymer were smaller than about 44.87 mJ/m².     

Modification of hydrophilic poly(vinyl alcohol) film via blending with hydrophobic poly(butyl acrylate-co-methyl methacrylate)

A series of poly(vinyl alcohol)/poly(butyl acrylate-co-methyl methacrylate) [PVA/P(BA-co-MMA)] blend films with different P(BA-co-MMA) content were prepared by the solution casting method. Surface morphologies of the PVA/P(BA-co-MMA) blend films were studied by scanning electron microscopy and atomic force microscopy. Thermal, mechanical, and chemical properties of PVA/P(BA-co-MMA) blend films were investigated by differential scanning calorimeter, thermogravimetric analysis, tensile tests, and surface contact angle tests. It was revealed that the introduction of P(BA-co-MMA) could affect the properties of the PVA films. The results also showed that, when P(BA-co-MMA) mole content is 3 %, the tensile strength and the surface contact angle of the polymer blend film are 20.4 MPa and 43.5°, respectively, suggesting that the polymer blend film holds both a better mechanical property and a better chemical property.     

Fully-biodegradable poly(3-hydroxybutyrate)/poly(vinyl alcohol) blend films with compositional gradient

Fully-biodegradable bacterial poly(3-hydroxybutyrate) (PHB)/chemosynthetic poly(vinyl alcohol) (PVA) blend films with compositional gradient from one surface to the other surface of the films were prepared by a dissolution-diffusion technique. Three kinds of PVA samples, high- and low-molecular weight atactic PVA and highly syndiotactic PVA (s-PVA), were used in order to investigate the effects of molecular weight and tactic structure on the generation of compositional gradient. The solution of PHB in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is also a good solvent for PVA, was cast on the PVA film and then the solvent HFIP was evaporated. By selecting the optimum volume of solvent and the evaporation rate, the PHB/PVA blend film with compositional gradient was obtained. The formation of compositional gradient was confirmed by FT-IR microscopy and ATR-FT-IR analysis. The 50%/50% PHB/s-PVA blend film with a nearly ideal compositional gradient, that is, the composition of PHB (or PVA) in the film changing gradually from 100% at one surface to 0% at the other surface of the film was obtained by casting PHB/HFIP solution on to the s-PVA film. Positional dependence of the absorbance of C==O and OH stretching bands along the film thickness direction for the PHB/S-PVA cast films.     

Surface dilational moduli of poly (ethylene oxide), poly (methyl methacrylate), and their blend films

Surface dilational moduli of poly (ethylene oxide) (PEO), poly (methyl methacrylate) (PMMA), and compatible PEO/PMMA blend films spread at the air-water interface were investigated as a function of surface concentration. The surface dilational modulus of an expanded PEO film increased as the surface concentration increased to 0.4mg/m(2), which corresponds to the limiting surface area of PEO. After peaking at this value, the surface dilational modulus decreased with an increase in the PEO concentration. Lissajous orbits of PEO films exhibited positive hysteresis loops for all surface concentration ranges. On the other hand, the surface dilational modulus of a condensed PMMA film steeply increased as the surface concentration increased. Lissajous orbits of PMMA films changed from positive hysteresis loops to negative loops at the surface concentration at which the surface pressure reached in the plateau region. The magnitude of the surface dilational modulus of PMMA was larger than that of PEO at a fixed surface concentration. The surface dilational moduli of the PEO/PMMA blend films increased with the total surface concentration and their magnitudes were less than those of the individual PMMA films and larger than those of the individual PEO films at fixed surface concentrations. Lissajous orbits of the PEO/PMMA blend films also changed from positive hysteresis loops to negative loops beyond the surface concentration at which the plateau surface pressure of PEO was attained.     

Polyelectrolyte blend multilayer films: surface morphology, wettability, and protein adsorption characteristics

We report the influence of polyelectrolyte (PE) multilayer films prepared from poly(styrene sulfonate)-poly(acrylic acid) (PSS-PAA) blends, deposited in alternation with poly(allylamine hydrochloride) (PAH), on film wettability and the adsorption behavior of the protein immunoglobulin G (IgG). Variations in the chemical composition of the PAH/(PSS-PAA) multilayer films, controlled by the PSS/PAA blend ratio in the dipping solutions, were used to systematically control film thickness, surface morphology, surface wettability, and IgG adsorption. Spectroscopic ellipsometry measurements indicate that increasing the PSS content in the blend solutions results in a systematic decrease in film thickness. Increasing the PSS content in the blend solutions also leads to a reduction in film surface roughness (as measured by atomic force microscopy), with a corresponding increase in surface hydrophobicity. Advancing contact angles (theta) range from 7 degrees for PAH/PAA films through to 53 degrees for PAH/PSS films. X-ray photoelectron spectroscopy measurements indicate that the increase in film hydrophobicity is due to an increase in PSS concentration at the film surface. In addition, the influence of added electrolyte in the PE solutions was investigated. Adsorption from PE solutions containing added salt favors PSS adsorption and results in more hydrophobic films. The amount of IgG adsorbed on the multilayer films systematically increased on films assembled from blends with increasing PSS content, suggesting strong interactions between PSS in the multilayer films and IgG. Hence, multilayer films prepared from blended PE solutions can be used to tune film thickness and composition, as well as wetting and protein adsorption characteristics.     

Surface dilatational moduli of poly(vinyl acetate) (PVAc) and PVAc-poly(n-hexyl isocyanate) (PHIC) blend films at the air-water interface

Surface dilatational moduli of poly(vinyl acetate) (PVAc) film and blend films of PVAc and poly(n-hexyl isocyanate) (PHIC) were measured at the air-water interface. PVAc formed a film that was looser and also more stable against strain than the PHIC film. The apparent surface dilatational modulus and surface pressure of the blend films were superimposed on the lower concentration of PVAc, irrespective of the composition of PVAc. However, the additivity rule was not applicable to the apparent surface dilatational modulus and surface pressure. The scaling exponents of the apparent surface dilatational modulus against the added surface concentration decreased with an increase in the proportion of PVAc, suggesting that blend films gradually change from glass material to expanded films.     

Rheo-optical FT-IR spectroscopy of poly(3-hydroxybutyrate)/poly(lactic acid) blend films

The orientation of poly(3-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) segments in PHB/PLA blend films cast from chloroform solutions with compositions PHB < PLA was studied during uniaxial elongation up to 250% strain at 50 °C by in-situ rheo-optical FT-IR spectroscopy. From the orientation functions of the ν(CO) bands of the blend components, it was derived that the PLA chains orient in the direction of elongation while the PHB chains orient perpendicular to the drawing direction. PHB homopolymer and PHB/PLA blend films with PHB > PLA compositions could only be oriented by cold drawing in ice water after quenching from the melt. The IR-dichroic effects of films drawn under these conditions indicate for both blend components a chain alignment parallel to the drawing direction.     

Effect of annealing on self-organized gradient film obtained from poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate)/poly(methyl methacrylate-co-n-butyl acrylate) blend latexes

The effect of annealing on the self-organized morphology and component gradient distribution of films prepared from bimodal latexes blend containing 1:1 silicon-containing acrylate copolymer/silicon-free acrylate copolymer blend was studied using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with X-ray energy-dispersive (SEM-EDX) spectrometry, and atomic force microscopy (AFM). The distribution of silicon through the whole thickness of the film as a function of annealing was investigated using confocal Raman spectroscopy (CRS). AFM results show that poly(methyl methacrylate-co-n-butyl acrylate) latex fuses to form a continuous film at 25?°C. The wettability of the acrylate components and the heterogeneous composition of poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate) result in a graded block film. ATR-FTIR and SEM-EDX measurements reveal silicon-containing components segregate at the film–air interface upon annealing. CRS further shows that the nonlinear model gradient distribution of silicon is obtained, where the content of silicon component is enhanced and it gradually varies in the bulk. When the annealing temperature increases to 120 and 180?°C, blend latexes films demonstrate varying topography and phase images, indicating phase separation is induced by annealing. Furthermore, CRS implies that the destruction of the gradient structure is attributed to the phase separation of the two blend components.     

Interfacial properties of hydrophilized poly(lactic-co-glycolic acid) layers with various thicknesses

Biodegradable polyesters such as poly(lactic-co-glycolic acid) copolymers (PLGA) are preferred materials for drug carrier systems although their surface hydrophobicity greatly limits their use in controlled drug delivery. PLGA thin films on a solid support blended with PEG-containing compound (Pluronic) were used as model systems to study the interfacial interactions with aqueous media. Degree of surface hydrophilization was assessed by wettability, and X-ray photoelectron spectroscopy (XPS) measurements. Protein adsorption behavior was investigated by in situ spectroscopic ellipsometry. The degree of protein adsorption showed a good correlation with the hydrophilicity, and surface composition. Unexpectedly, the layer thickness was found to have a great impact on the interfacial characteristics of the polymer films in the investigated regime (20-200 nm). Thick layers presented higher hydrophilicity and great resistance to protein adsorption. That special behavior was explained as the result of the swelling of the polymer film combined with the partial dissolution of Pluronic from the layer. This finding might promote the rational design of surface modified biocompatible nanoparticles.     

Micro construction of poly(epsilon-caprolactone)/poly(L-lactic acid) blend film by solution casting under microwave irradiation

The micro construction of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres. The weight loss caused by degradation of the PCL/PLLA blend obtained by conventional methods (B50c) is greater than that of the blend obtained by microwave methods (B50m), which reflects the change in morphology from a loose PCL network (B50c) to a dense PCL plank (B50m).     

Properties of poly(lactic acid-co-glycolic acid) film modified by blending with polyurethane

A number of poly(lactic acid-co-glycolic acid)/polyurethane (PLGA/PU) blend films with various PU mole contents were prepared by casting the polymer blend solution in chloroform. The surface morphologies of the PLGA/PU blend films were studied by scanning electron microscopy (SEM). The thermal, mechanical and chemical properties of the PLGA/PU blend films were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile tests and surface contact angle tests. The results revealed that the introduction of PU could markedly modify the properties of PLGA films.     

Phase separation in poly(tert-butyl acrylate)/polyhedral oligomeric silsesquioxane (POSS) thin film blends

Phase separation in thin film blends of poly(tert-butyl acrylate) (PtBA) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), is studied as functions of annealing temperature and time, using reflected light optical microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The results demonstrate that the PtBA/TPP blend system confined to thin films ( approximately 90 nm) exhibits lower critical solution temperature (LCST) behavior with a critical temperature of approximately 70 degrees C and a critical composition of 60 wt % PtBA with insignificant dewetting at the phase boundary. Off-critical spinodal behavior is observed for 58 and 62 wt % PtBA blend films. Phase separation by nucleation and growth is observed for all compositions outside the window between 58 and 62 wt % PtBA. The temporal evolution of spinodal decomposition in 60 wt % PtBA blend films is explored at annealing temperatures of 75, 85, 95, and 105 degrees C. The morphological evolution in 60 wt % PtBA blend films is similar for all experimental temperatures (75, 85, 95, and 105 degrees C) with the expected shorter time scales for phase evolution at higher annealing temperatures. Fast Fourier transforms of optical micrographs reveal that these blend films immediately undergo phase separation by spinodal decomposition during temperature jump experiments. Power law scaling for the characteristic wavevector with time (q approximately t(n) with n approximately -1/4 to -1/3) for domain growth during the early stages of phase separation yields to domain pinning at the later stages for 60 wt % PtBA blend films annealed at 75, 85, and 95 degrees C. In contrast, domain growth is pinned over the entire experimental time scale for 60 wt % PtBA blend films annealed at 105 degrees C.     

Twisted nematic LC mode with high electro-optical performance and high thermal endurance formed using IB-irradiated poly(methyl methacrylate) as an alignment layer

We obtained homogeneously aligned liquid crystals (LCs) on ion beam (IB) irradiated poly(methyl methacrylate) (PMMA) by controlling the IB energy. We then examined the LC alignment state using polarized optical microscopy and conducted thermal stability testing. We obtained homogeneous LC alignment at IB energies above 1,400 eV, indicating that strong IB energy facilitates the alignment of LCs on the PMMA surface. This surface was analyzed by atomic force microscopy, and the contact angles (CAs) were measured to elucidate the mechanism of LC alignment. The increased surface energy strengthened the van der Waals interaction between the surface and LCs, thereby inducing stable, homogeneous LC alignment. Electro-optical (EO) characteristics were measured using twisted nematic (TN) LC mode. Compared to LC cells with conventionally used rubbed polyimide (PI), the LC cells with IB-irradiated PMMA exhibited higher thermal budgets and good electro-optical characteristics. These new LC cells have promising potential for advanced LC displays.     

Morphology-driven surface segregation in a blend of poly(epsilon-caprolactone) and poly(vinyl chloride)

A blend of poly(epsilon-caprolactone) (PCL) and poly(vinyl chloride) (PVC) with 90 wt % PCL was prepared. Two films of this blend, which were grown at 35 and 45 degrees C, showed the absence and presence of banded spherulites, respectively. A detailed examination conducted with time-of-flight secondary ion mass spectrometry (ToF-SIMS) found that the surface composition of the film grown at 45 degrees C was related to its structure, which was shown to contain ridges and valleys. Phase images obtained using atomic force microscopy (AFM) indicated that the ridges and valleys consisted of edge-on and flat-on lamellae, respectively. ToF-SIMS imaging revealed that PVC and PCL were located mainly on the surface of the valleys and ridges, respectively. This morphology-driven surface segregation was caused by the difference in the surface energy between the flat-on and edge-on lamellae.     

Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques. At the surface pressure below 10 mN/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide). At higher surface pressures, the results obtained indicate the desorption of poly(propylene oxide) segments from the monolayer and their interaction with poly(ethylene oxide) segments in an aqueous phase. At a surface pressure close to 19 mN/m, the behavior of adsorbed and spread poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) films becomes different. The real part of dynamic surface elasticity of spread films tends toward its maximum value (20 mN/m) and, upon further compression, films begin to dissolve. At the same time, the surface elasticity of adsorbed films decreases nearly twofold upon the achievement of the maximum value that testifies the formation of looser structure of the surface layer.     

Biodegradable hybrid polymer films based on poly(vinyl alcohol) and collagen hydrolyzate

Hybrid blends of poly(vinyl alcohol) (PVA) and collagen hydrolyzate (CH), an added value waste from leather indutry, have been converted by blown molding extrusion, to environmentally degradable films. Blown extruded films comprising 5-15% of CH, were tested as sel fertilizing mulching films and analyzed for their propensity to enviromental degradation. PVA/CH films rapidly disintegrate when buried in soil, and resulted promising for application such as transplanting films, with additional fertilizing action of CH.